Aberdyfi-Harlech 33kV Reinforcement

Aberdyfi-Harlech 33kV Reinforcement ED2 Engineering Justification Paper

ED2-LRE-SPM-004-CV1-EJP

Issue Date Comments

Issue 0.1 Jan 2021 Issue to SRG and external assurance

Issue 0.2 Apr 2021 Reflecting comments from SRG

Issue 0.3 May 2021 Reflecting assurance feedback

Issue 1.0 Jun 2021 Draft Business Plan Submission

Issue 1.1 Oct-21 Reflecting updated DFES forecasts

Issue 1.2 Nov-21 Reflecting updated CBA results

Issue 2.0 Dec 2021 Final Business Plan Submission

Scheme Name Aberdyfi-Harlech 33kV Reinforcement

Activity 33kV Network Reinforcement

Primary Investment Driver Voltage Constraints

Reference ED2-LRE-SPM-004-CV1-EJP

Output Load Index

Cost £4.750m

Delivery Year 2023-28

Reporting Table CV1

Outputs included in ED1 Yes/No

Business Plan Section Develop the Network of the Future

Primary Annex Annex 4A.2: Load Related Expenditure Strategy: Engineering Net Zero Annex 4A.6: DFES

Spend Apportionment ED1 ED2 ED3

- £4.750m -

ED2-LRE-SPM-004-CV1-EJP – Aberdyfi-Harlech 33kV Reinforcement

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Technical Governance Process

Project Scope Development IP1(S)

To be completed by the Service Provider or Asset Management. The completed form, together with an accompanying report, should be endorsed by the appropriate sponsor and submitted for approval. IP1 – To request project inclusion in the investment plan and to undertake project design work or request a modification to an existing project IP1(S) – Confirms project need case and provides an initial view of the Project Scope IP2 – Technical/Engineering approval for major system projects by the System Review Group (SRG) IP2(C) – a Codicil or Supplement to a related IP2 paper. Commonly used where approval is required at more than one SRG, typically connection projects which require connection works at differing voltage levels and when those differing voltage levels are governed by two separate System Review Groups. IP2(R) – Restricted Technical/Engineering approval for projects such as asset refurbishment or replacement projects which are essentially on a like-for-like basis and not requiring a full IP2 IP3 – Financial Authorisation document (for schemes > £100k prime) IP4 – Application for variation of project due to change in cost or scope PART A – PROJECT INFORMATION

Project Title: Aberdyfi-Harlech 33kV Reinforcement Project Reference: ED2-LRE-SPM-004-CV1-EJP Decision Required: To give concept approval to install STATCOM at Aberdyfi and Mechanically Switched Capacitor Bank at

Harlech 33kV substations along with operational management via flexibility services during project delivery

Summary of Business Need: The Aberystwyth and Rhydlydan area of the SP Manweb (SPM) network supplies over 22,600 customers predominantly fed from long overhead line circuits. The group is presently at voltage limits and network suffers from marginal voltages excursions outside of statutory limits and is presently being operationally managed. Studies indicate that with the additional demand growth and LCT uptake will lead to steady state and voltage step issues beyond operational management in the network around Aberystwyth, Aberdyfi, Machynlleth, Tywyn, Fairbourne, Barmouth, Dyffryn Ardudwy and Harlech for N-1 33kV outages during periods of high demand and low generation. With the demand growth network will potentially be “Non-Compliant” and it is proposed to carry out system reinforcement in the RIIO-ED2 price control period in order to accommodate future demand growth within the area, secure supplies within the group, meet the licence obligations under EREC P2/7 – Security of Supply, maintain the steady state voltage of the 33kV network to within ± 6% of the declared voltage under the ESQCR 2002 and maintain voltage step within ±10%. The SPM DFES forecasts a significant number of LCTs including 4.8k Electric Vehicles and 4.2k Heat Pumps. Summary of Project Scope, Change in Scope or Change in Timing: An innovative reactive power compensation scheme is proposed which comprises of a STATCOM and Mechanically Switched

Capacitor Bank (MSC). The proposed scheme includes:

• Installation of ±10MVAr STATCOM with associated 33/11kV transformer at Aberdyfi primary substation, and extension of 33kV board with one breaker.

• Installation of 5MVAr MSC and replace the 33kV AIS breakers with 5-panel switchboard at Harlech primary substation.

• Contract with flexibility services to support during project delivery

• Total scheme cost – £4.750m (2020/21 prices), which is fully funded by SPEN in the ED2 period.

Expenditure Forecast (in 2020/21 prices) Licence

Area Reporting

Table Description Total (£m)

Incidence (£m) 2023/24 2024/25 2025/26 2026/27 2027/28

SPM CV1 Primary Reinforcement 4.613 0.231 0.461 1.153 1.384 1.384 SPM CV1 Flexibility Services 0.138 0.002 0.025 0.013 0.098 -

Total Cost 4.750 0.233 0.486 1.166 1.482 1.384

PART B – PROJECT SUBMISSION

Proposed by Kailash Singh Signature Date: 30/11/2021

Endorsed by Russell Bryans Signature Date: 30/11/2021

PART C – PROJECT APPROVAL

Approved by Malcolm Bebbington Signature Date: 30/11/2021


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Contents Technical Governance Process ............................................................................................................................... 1

1 Introduction ........................................................................................................................................................ 3

2 Background Information .................................................................................................................................. 5

3 Needs Case ......................................................................................................................................................... 7

4 Optioneering .................................................................................................................................................... 11

5 Detailed Analysis .............................................................................................................................................. 12

6 Deliverability & Risk ........................................................................................................................................ 18

7 Conclusion ........................................................................................................................................................ 22

8 Appendices ........................................................................................................................................................ 23


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1 Introduction The SP Manweb (SPM) network in Mid Wales around the Aberystwyth, Fairbourne, Tywyn, Machynlleth, Llanrhystud, Llanilar and Glanyrafon is supplied from Swansea North GSP within the Western Power Distribution (WPD) license area. The 132kV network group secures Aberystwyth Rhydlydan 33kV group supplying over 22,605 customers which includes a major industrial area in Glanyrafon and several recreational/tourist destinations spread across the network. Figure 1-1 shows the SPM 132kV and 33kV network area fed from Aberystwyth/Rhydlydan and adjacent Maentwrog grid network.

Figure 1-1: 132kV and 33kV network area

The group is presently at voltage limits set out in the Electricity Safety Quality and Continuity Regulations (ESQCR). Within the RIIO-ED1 period the network suffers from marginal voltages excursions outside of statutory limits which is presently being operationally managed by temporarily moving the split point from Fairbourne to Tywyn to supply some load from the adjacent Four Crosses GT2 / Maentwrog GT1 / Maentwrog GT2 group. With the additional demand associated with LCT uptake within the RIIO-ED2 period these voltage excursions will aggravate and will be beyond operational management. To maintain voltages within statutory limits it is proposed to carry out system reinforcement in the RIIO-ED2 price control period. An innovative reactive power compensation scheme is proposed which comprises of a STATCOM and a Mechanically Switched Capacitor Bank (MSC). The proposed scheme includes:


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• Extension of 33kV board with one breaker and installation of ±10MVAr STATCOM with associated 33/11kV transformer at Aberdyfi substation.

• Replacement of existing 33kV outdoor breakers with 5-panel switchboard at Harlech and installation of 5MVAr MSC.

The voltage constraints in this group are both steady state and voltage step. These voltage step issues cannot be mitigated through flexibility as the mitigation needs to be fast acting in real-time. Thus, it is proposed to use flexibility services to minimize the steady-state network risk and support during the project delivery. We will continue to tender for flexibility services in this area to test the market for technically compliant flexibility solutions to resolve this complex voltage constraint. It is proposed to start the works in 2023/24 and the capacity release of 15MVA between the two 33kV groups will be claimed in 2027/28 at the end of the project. The timing of the project is based on delivering the highest NPV, while managing the network risk via operational management through flexibility services during project delivery. Total scheme cost – £4.750m (2020/21 prices) with 100% contribution to be included in the RIIO-ED2 load related expenditure.


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2 Background Information

2.1 Existing/Authorised Network The existing 33kV network comprises a long overhead line circuits and is supplied by two grid transformers located Aberystwyth (60MVA) and Rhydlydan (45MVA). The 33kV group is supplied from the Swansea North GSP through the 2 x 132kV circuit from WPD’s Rhos 132kV substation. The capacity of the grid transformer at Aberystwyth grid is restricted to 45MVA considering the grid transformer tails rating. The 33kV network group secures HV network comprising of 12 primary transformers and these primary transformers supply 22,605 customers. The 33kV group has interconnection via 2 x 33kV circuits with adjacent Maentwrog grid fed from Trawsfynydd GSP, considering the angular difference between GSPs the interconnection is split at Fairbourne and Machynlleth. However, during 33kV outages around 3000 customers are transferred to Maentwrog grid side by temporarily moving the split point to Aberdyfi and during 33kV outage from Maentwrog grid side around 10,000 customers supplied from Harlech, Dyffryn Ardudwy, Barmouth, Dolgellau, Machynlleth T2 and Cammaes Road are transferred to the Aberystwyth side by closing the split points. The authorised 33kV Aberystwyth/Rhydlydan group network is shown in Figure 2.1.

Aberdyfi

R

Aberystwyth Grid

R

R

R

Machynlleth

R

R

R

North Road

A

A

Llanilar

Fferm Wynt

Llangwyryfon

A

A

A

Rhydlydan Grid

Rheidol

Power Station

17kms

26kms

26kms

5.5kms

13kms

24kms

GT1

60MVA

A

A

G2

15MW

A

Harlech

11kV

4MVA

Dyffryn

Ardudwy

Dolgellau

R

R

Cemmaes

Road

Fferm

Wynt

Cemmaes

11kV

4MVA

G1

15MW

GT2

60MVA

Maentwrog

Grid12kms

10kms

21kms

Figure 2.1: Authorised Aberystwyth/Rhydlydan 33kV network

2.2 Network supply / circuit capacity

The existing 33kV Aberystwyth/Rhydlydan network is classed as P2/7 Group C (≥10MW up to 60MW)

Table 2-1 presents the existing network supply capacity of the 33kV group.

Table 2-1: Summary of authorised EHV group network

Substation No. of

customers (#) Scenario

LI firm capacity (MVA)

Maximum demand (MVA)

Load Index

Group P2/7 Class

EHV

Aberystwyth GT1 / Rhydlydan GT1

22605 N-1 45.4 39 LI2 C


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2.3 Embedded Generation

The 33kV group network has significant penetration of distributed generation with 80.4MW connected generation as shown in Table 2-2. The network area has seen a significant generation connection interest which is restricted by capacity limitations on the NGET and WPD 132kV network and all new generation connections in the Aberystwyth/Rhydlydan network area are subject to Modification application to NGET and WPD. An advanced RIIO-ED1 Constraint Management Zone is in delivery in this area, for more information see Annex 4A.3, our DSO strategy. Table 2-2: Embedded generation in Aberystwyth/Rhydlydan 33kV group

Site Status Type Registered capacity

(MW) Rheidol Wind Farm Connected Onshore wind 2.5

Rheidol Connected Hydro 41.0 Mynydd Gorddu Connected Onshore wind 10.2

Morfa Camp Connected Solar 2.3 Llangwyryfon Wind Farm Connected Onshore wind 9.4

Dinas Dam Connected Hydro 13.5 Cwm Rheidol Connected Hydro 1.5

Total 80.4

2.4 Fault levels

There are no fault level related constraints in the 33kV group network.


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3 Needs Case The 33kV Aberystwyth/Rhydlydan network supplies 22,605 customers cover widespread supply area (>800km²) which is part of the Gwynedd county in the North Wales. The generation is not uniformly distributed across the group and the demand is supplied via long overhead line circuits. Aberystwyth/Rhydlydan network group is presently at voltage limits and network suffers from marginal voltages excursions outside of statutory limits and are being operationally managed. With the anticipated demand growth and uptake of LCTs these voltage excursions will be lower the primary transformer tap range limits and cannot be operationally managed. The network will be “Non-Compliant” and it is proposed to carry out system reinforcement in the RIIO-ED2 price control period in order to accommodate future demand growth within the area, secure supplies within the group, meet the licence obligations under EREC P2/7 – Security of Supply, maintain the steady state voltage of the 33kV network to within +/- 6% of the declared voltage under the ESQCR 2002 and maintain voltage step within +/- 10%. Further to comply with section 9 of the Electricity Act and Condition 21 of our license obligation “to develop and maintain an efficient, coordinated and economical system for the distribution of electricity” an enduring design solution is required in order to satisfy the existing customer requirements and accommodate future load growth. This concept paper covers the 33kV network solutions required to mitigate the voltage violations.

3.1 Existing voltage excursions The group is presently at voltage limits and network suffers from marginal voltages excursions outside of statutory limits. Studies indicate that for an outage of the 33kV circuit from Aberystwyth to Aberdyfi in periods of high demand and low generation, there are voltages are marginally below the primary transformer tap changer range. At present this situation is operationally managed by temporarily moving the split point from Fairbourne to Tywyn to supply some load from the adjacent Four Crosses GT2 / Maentwrog GT1 / Maentwrog GT2 group. The actual historical measured voltage profile at Fairbourne is shown in Figure 3.1.

Figure 3.1: Actual measured voltage at Fairbourne 33kV substation

3.2 Forecast Demand

The DFES includes granular forecasts to 2050 for demand, generation and Low Carbon Technologies (LCTs). They assess four credible future scenarios covering a range of uncertainties, including: differing levels of consumer ambition, policy support, economic growth and technology development and the forecasts are underpinned by extensive stakeholder engagement.


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This forecast is based on actual system measurement data from the PI system and stakeholder endorsed Distribution Future Energy Scenarios (DFES) and considers our pipeline of known developments.

3.2.1 Local Considerations and stake holder feedback As part of our DFES scenario development SPEN held stakeholder engagement sessions with councils to continue to refine our understanding of their economic growth plans and other drivers. This helps determine the resultant demand increase and impact on our network.

3.2.1.1 Electric Vehicles Charging Strategy In December 2020, Welsh Government published their electric vehicles charging strategy1 to facilitate transition of Wales towards Net-Zero in-line with UK Government’s targets with a vision that by 2025, all users of electric cars and vans in Wales are confident that they can access electric vehicle charging infrastructure when and where they need it. Welsh Government to invest in public charging infrastructure to at least meet the demand created by 60% of new sales for cars and vans being electric vehicles by 2030. Welsh Government is proposing to invest in the region of £30m over the next five-year period on electric vehicle charging to make this strategy happen. Welsh Government predicts 32,000 EVs by 2025 and 135,000 EVs by 2030 in the SPM network license area. 3.2.2 Distribution Future Energy Scenarios The system is forecast exceed network capacity within the ED2 period. This forecast is based on actual system measurement data from the PI system and stakeholder endorsed Distribution Future Energy Scenarios (DFES) and considers our pipeline of known developments. The winter demand forecast based on the future energy scenarios along with the projected demand from authorised connections is shown in Figure 3.2.

Figure 3.2: Demand forecast for the Aberystwyth/Rhydlydan group

The anticipated residential electric vehicle and heat pump uptake based on the future energy scenarios is presented in Figure 3.3.

1 https://gov.wales/sites/default/files/consultations/2020-12/electric-vehicle-charging-strategy-consultation-document.pdf


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Figure 3.3: Electric Vehicles and Heat Pump uptake profile for the Aberystwyth/Rhydlydan group

3.2.3 Best View Scenario For the Aberystwyth/Rhydlydan group demand, the forecast demand growth under our Baseline scenario, along with the firm capacity and utilisation through to RIIO-ED3 period is shown in Table 3-1. Table 3-1: Baseline View forecast

Year

202

1

202

2

202

3

202

4

202

5

202

6

202

7

202

8

202

9

203

0

203

1

203

2

203

3

Winter (N-1)

Forecast Demand (MVA) 39 40 41 42 43 44 46 48 51 53 56 59 62 Firm Capacity (MVA) 45 45 45 45 45 45 45 45 45 45 45 45 45 Utilisation (%) 87 89 92 93 96 99 103 107 112 118 125 131 138 Load Index LI2 LI2 LI2 LI2 LI3 LI3 LI5 LI5 LI5 LI5 LI5 LI5 LI5

3.3 Network Impact Assessment

Detailed network studies covering Intact, N-1 and fault level assessments were conducted for the 33kV network considering the different demand forecast scenarios. The findings from the network impact assessments are detailed in sections below. 3.3.1 Thermal Constraints There were no thermal constraints in the Aberystwyth/Rhydlydan 33kV network. 3.3.2 Voltage Constraints and security of supply System studies indicate that for an outage of 33kV circuit from Aberystwyth – Aberdyfi, Maentwrog - Harlech and outage of grid transformer at Aberystwyth the network will foresee steady state and voltage step violations. The voltage excursions at several 33kV substations will be well below the primary transformer tap changer range and will be beyond operational management leading to significant CI/CML impact with security of supply issues to over 20000 customers. The steady state and voltage step violations for most onerous outage at 33kV substations is shown in Table 3-2. Table 3-2: 33kV network voltage violations

Substation Most Onerous Violation Type

Calculated voltage (pu)

Limit(pu) Outage

Aberdyfi Voltage Step 0.78 0.90

Aberystwyth -Aberdyfi Circuit

Tywyn Voltage Step 0.77 0.90

Fairbourne Voltage Step 0.76 0.90 Mynydd Gorddu Voltage Step 0.89 0.90

Machynlleth Voltage Step 0.83 0.90 Aberystwyth Voltage Step 0.90 0.90

Aberystwyth GT Parc-y-llyn Voltage Step 0.90 0.90

Barmouth Steady State 0.91 0.94 Maentwrog-Harlech Ckt / Voltage Regulator(VR) under maintenance

Harlech Steady State 0.90 0.94 Maentwrog-Harlech Ckt with Voltage Regulator(VR) under maintenance


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3.3.3 Fault Level Constraint There are no fault level related constraints. 3.3.4 Network Risk and Flexibility Network studies identified the risk in terms of the voltage excursions with the forecast demand and the anticipated duration of the risk. Further a time profile-based simulation (17520 simulations/year) were performed considering the historical half hourly measured SCADA data combined with the DFES demand projections. These considered each year through the RIIO-ED2 price control period to identify the potential risk duration and risk window. The half-hourly studies performed for years starting from 2023/24 through 2027/28 helped identify the anticipated time of risk on the network as well as the flexible capacity required to alleviate the constraints on the network. The key results from the half hourly profile-based simulations are furnished in Appendix - 8.1. Profile based studies indicate that the under-voltage risk potential starts from the beginning of RIIO-ED2 and with a combination of operational mitigation these risks can be minimised, however cannot be alleviated. The capacity required with a combination of operational management would be ca. 2.5MW and 2.5MVAr by 2028. Table 3-3 below shows the network risk hours calculated in combination with operational management, tendered capacity and qualified capacity from the connected/future customers in the group. Table 3-3: Network risk duration and Flexible Capacity (MW)

Year 2023/24 2024/25 2025/26 2026/27 2027/28

Risk Duration (Hrs) 27 43.5 104.5 509 1194

Required Flexible Capacity (MW) 1.3 1.8 1.9 2.0 2.5

Required Flexible Capacity (MVAr) 1.4 1.8 1.9 2.1 2.5

Received Flexible capacity (MW) 1.2 2.9 1.6 2.9 1.65

Received Flexible capacity (MVAr) - - - - -

Flexible MW capacity met (%) 92% 162% 87% 141% 66%

Cost(£m) 0.00 0.02 0.01 0.10 -


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4 Optioneering Table 4-1 shows the long list of options considered for the scheme. Few of the longlist options are rejected based on the technical and commercial rustications and the reasons are provided in the table. Option 2, reactive compensation at Aberdyfi and Harlech primary substations is the minimum required scheme to mitigate the voltage issues in the 33kV group. The shortlisted options are taken forward for detailed analysis and included in the cost-benefit analysis. Table 4-1: Long list of options considered

Option Description Status Reason for rejection

(a) No Intervention Rejected Not compliant with ESQCR, Distribution code limits and security of supply requirements as per P2/7.

(b) Intervention plan using only Energy Efficiency

Rejected Discounted due to lower cost effectiveness (peak MW reduction per £) and the number of individual interventions required across the wide area supplied by this network.

(c)

Permanent interconnection with Maentwrog/Four Crosses grid network by “Normally Close” the split point at Fairbourne.

Rejected

Due to the phase angle difference between the GSP groups, the permanent interconnection would lead to potential trips due to the thermal overloads on the circuit between Maentwrog to Harlech. This would potentially increase the security supply risk to customers and have significant CI/CML impact.

(d)

Transfer of Tywyn and Fairbourne primary substations to Maentwrog/Four Crosses group by shifting the “Normally Open” point to Aberdyfi.

Rejected

With the increased demand this option will be not compliant with ESQCR, Distribution code limits and security of supply requirements as per P2/7 as the voltage’s issues will not be alleviated. Further during a maintenance outage of Maentwrog-Harlech circuit followed by outage of Aberystwyth GT would lead to loss of supplies to the complete group network.

(e) Management of voltage constraints using flexibility services

Rejected

The voltage constraints in this group are both steady state and voltage step. From the flexibility tender rounds only MW capacity bids have been received which are predominantly aggregation of domestic EV chargers. The group voltage step issues cannot be mitigated through the received flexibility services as the mitigation need to be in near real-time. However, considering the increased risk during by end of RIIO-ED2 period, flexibility services can be utilised during project delivery as proposed in Option 2. We will continue to tender for flexibility services in this area in order to test the market for technically compliant flexibility solutions to resolve this complex voltage constraint.

(f)

New 33kV circuit between Aberystwyth to Aberdyfi 33kV substation along with installation of MSC at Harlech.

Considered (Baseline)

-

(g)

New 33kV circuit between Bow Street to Aberdyfi 33kV substation along with installation of MSC at Tywyn and Harlech.

Considered (Option 1)

-

(h)

Installation of Phase Shifting Transformer (PST) at Aberdyfi to enable permanent interconnection with Maentwrog/Four Crosses group.

Rejected

With the increased demand this option will be not compliant with ESQCR, Distribution code limits and security of supply requirements as per P2/7 as the voltage’s issues will not be alleviated by permanent interconnection via PST.

(i) Installation of ±10MVAr STATCOM at Aberdyfi and 5MVAr MSC at Harlech.


-

(j) New 132/33kV grid infeed at Aberdyfi.


-

(k) New 132/33kV grid infeed at Machynlleth.

Rejected The 132/33kV grid transformer at Machynlleth will not alleviate the constraints and would need additional 33kV interconnections.

(l) HVDC back to back convertor at Machynlleth.

Rejected The overall scheme cost for back to back HVDC convertor will be significantly higher with a long lead time.

(m) MVDC back to back convertor at Aberdyfi.

Rejected The overall scheme cost for back to back MVDC convertor considering 33kV circuit uprating’s >30kms will be significantly higher and will have a long lead time.


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5 Detailed Analysis The demand and generation are not uniformly distributed across the group with primary transformer substations being supplied by reasonably long or high impedance 33kV circuits which can lead to voltage issues. Steady state under-voltage and voltage step issues were identified at several substations within the 33kV group. System studies indicate that these under voltage issues cannot be operationally managed and reactive power support would be required within RIIO-ED2 price control period.

5.1 Proposed solution - ±10MVAr STATCOM at Aberdyfi and 5MVAr MSC at Harlech along with flexibility services (Option 2)

To mitigate the voltage issues in the group, it is proposed to install a new reactive support device at the existing Aberdyfi 33kV substation. Studies have been undertaken to assess a wide range of options in both location and static/dynamic voltage support. Aberdyfi is identified the most suitable location for fast-acting dynamic MVAr support in the form of a ±10MVAr STATCOM to manage voltage step issues. Additionally, installation of 5MVAr of reactive support in the form of a capacitor at Harlech is required to support the steady voltage during outages at Maentwrog. Together these mitigate both steady state and voltage step issues in the group through ED2 and ED3. The STATCOM solution is a ‘smart’ solution, comprises of a DC capacitor behind a power electronics voltage source converter to act as either a sink or source of reactive power. This provides fast acting, controllable voltage regulation. The STATCOM device would likely be controlled to 0 MVAr output during Intact conditions and provide reactive power support during contingent conditions. Cost estimates at this stage include for provision of a ±10 MVAr STATCOM. At Aberdyfi it is proposed to extend the existing 33kV switchboard to accommodate circuit breaker for STATCOM which will be connected via dedicated 33/11kV transformer. The layout and line diagram of the proposed STATCOM solution is shown in Appendix 8.2. At Harlech there is space to accommodate the 5MVAr MSC, considering the existing switchgear capability against the capacitor switching transients it is proposed to replace existing outdoor switchboard with a 5-panel board with modern breakers and to reduce the overall site footprint it is proposed to install Metal Enclosed Capacitor Bank (MECB) with 2 steps of 2.5MVAr each. The typical arrangement of MECB is shown in Appendix 8.2. The overall network with the proposed is shown in Figure 5.1 and the costs of works under the proposed option is shown in Table 5-2.

Aberdyfi

R

Aberystwyth Grid

R

R

R

Machynlleth

R

R

R

North Road

A

A

Llanilar

Fferm Wynt

Llangwyryfon

A

A

A

Rhydlydan Grid

Rheidol

Power Station

A

Harlech11kV7.5MVA

Dyffryn

Ardudwy

To

Maentwrog

Grid

±10MVAr

STATCOM

2x2.5MVAr

Capacitor Bank

11kV

Previously Authorised

System split point

Third party Owned

Recoveries

Proposed works in ED2

Figure 5.1: Proposed works in the Aberystwyth/Rhydlydan 33kV group


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The increase in capacity and cost of flexibility, due to demand growth, was considered against the benefit of deferral in each year of RIIO-ED2. This is assessed using flexibility to manage the constraint while the level and number of risk hours is relatively low, to commission the above proposed works when efficient to do so. The cost of flexibility for 2023/24 to 2026/27 considering 50% utilization based on the recent tenders for a total of 8.7MW is shown in Table 5.1 Table 5.1. Summary of flexibility service costs

Year 2023/24 2024/25 2025/26 2026/27 2027/28

Qualified Flexibility Services (MW) 1.2 2.9 1.6 2.9 1.65

Cost of Flexibility Services £0.002m £0.025m £0.013m £0.098m Not enough capacity

Annual Reinforcement Deferral Cost(£m) 0.175 0.175 0.175 0.175 0.175

Flexibility Outlook

Accept flexibility bids and defer reinforcements Reject flexibility bids and deliver reinforcements

Considering the above it is proposed to start the reinforcement works in 2023/24 and the capacity release of 15MVA will be claimed in 2027/28 at the end of the project. The estimated cost for the above is £4.750m (in 2020/21 prices) with 100% contribution to be included in the RIIO-ED2 load related expenditure. The voltage constraints in this group are both steady state and voltage step. These voltage step issues cannot be mitigated through flexibility as the mitigation needs to be fast acting in real-time. Thus, it is proposed to use flexibility services to minimize the steady-state network risk and support during the project delivery. We will continue to tender for flexibility services in this area to test the market for technically compliant flexibility solutions to resolve this complex voltage constraint. Table 5-2: Proposed solution costs

Asset Description Volumes Prime Costs

(£m) RIIO-ED2

Contribution(£m) 6.6/11kV CB (GM) Primary 1 0.028 0.028

33kV UG Cable (Non-Pressurised) 0.15 0.036 0.036 33kV CB (Gas Insulated Busbars)(ID) (GM) 5 0.852 0.852 33kV Transformer (GM) 1 0.314 0.314

Batteries at 33kV Substations 1 0.009 0.009 ±10MVAr STATCOM at Aberdyfi 1 2.500 2.500

2x2.5MVAr MSC at Harlech 1 0.250 0.250 Civil Works at 33 kV & 66 kV Substations 0.381 0.381

Wayleaves/Easements/Land Purchase 0.075 0.075 Other Costs (Identify Below) 0.167 0.167

Cost of flexibility services 0.138 0.138 Total Costs 4.750 4.750

Detailed Dynamic Compensation and Power Quality assessment studies - £25k Environmental considerations and Design & Engineering Studies – £70k

Associated protection, control or SCADA equipment - £72k


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5.2 Baseline – New 33kV ckt between Aberdyfi & Aberystwyth and MSC at Harlech

The Baseline option involves installing a new ca. 18km long 33kV circuit between Aberystwyth Grid and Aberdyfi primary substation and reactive compensation in the form of 2x1.5MVAr capacitor banks at Harlech primary substation. The option also required additional 33kV switchgear to accommodate the 33kV reinforcements. The total cost of the scheme is £9.083m. The additional circuit path to Aberdyfi will reduce the electrical distance in the Aberystwyth – Aberdyfi – Machynlleth 33kV ring. Combinedly with the reactive compensation at Harlech would alleviate the voltage constraints in the 33kV group. Table 5-3 and Table 5-4 provides the scheme summary and cost & volume breakdown correspondingly. Figure 5.2 show the works included under the Baseline option. Table 5-3: Baseline scheme summary

Category Scheme Name

Scheme Summary RIIO-ED2

Contribution (£m)

Customer Contribution

(£m)

Circuit & Substation

Aberdyfi-Harlech 33kV Reinforcement

1.Extension of Aberystwyth 33kV switchboard and New 33kV circuit between to Aberdyfi 33kV substation - 18kms 400 sq. mm XLPE AL Cable. 2. Installation of 2x1.25MVAr Mechanically Switched Capacitor Bank at Harlech 33kV substation

£9.083 -

Figure 5.2: Works in Aberystwyth/Rhydlydan 33kV group under Baseline Table 5-4: Baseline costs and volumes


(£m) RIIO-ED2

Contribution(£m) 33kV UG Cable (Non-Pressurised) 18.05 4.379 4.379

33kV CB (Gas Insulated Busbars)(ID) (GM) 7 1.193 1.193 33kV Switch (GM) 1 0.047 0.047

Pilot Wire Underground 18 1.994 1.994 2x1.25MVAr MSC at Harlech 1 0.200 0.200

Civil Works at 33 kV & 66 kV Substations - 0.320 0.320 Wayleaves/Easements/Land Purchase - 0.500 0.500

Other Costs (Identify Below) - 0.450 0.450 Total Costs 9.083 9.083

Power Quality assessment studies - £25k Environmental considerations and Design & Engineering Studies – £325k Associated protection, control, or SCADA equipment -£100k


15

5.3 Option 1 – New 33kV Aberdyfi -Bow Street Circuit and MSCs at Tywyn and Harlech

The Option 1 involves installing a new ca. 12km long33kV circuit between Aberystwyth Grid and Bow Street primary substation and reactive compensation at Tywyn (5MVAR MSC) and Harlech (2.5MVA MSC) primary substation. The option also required additional 33kV switchgear to accommodate the 33kV reinforcements. The total cost of the scheme is £10.062m. Similar to the Baseline option, the additional circuit path to Bow Street will reduce the electrical distance in the Aberystwyth – Aberdyfi – Bow Street -Machynlleth 33kV ring. Combinedly with the reactive compensation at Tywyn and Harlech would alleviate the voltage constraints in the 33kV group. Table 5-5 and Table 5-6 provides the scheme summary and cost & volume breakdown correspondingly. Figure 5.3 show the works included under the Option 1. Table 5-5: Option 1 summary



Contribution (£m)


(£m)



1.Extension of Bow Street and New 33kV circuit between Bow Street and Aberdyfi 33kV substation - 12kms 400 sq. mm XLPE AL Cable. 2. Installation of 5MVAr Mechanically Switched Capacitor Bank at Tywyn 33kV substation 3. Installation of 2x1.25MVAr Mechanically Switched Capacitor Bank at Harlech 33kV substation

£10.062 -

Figure 5.3: Works in Aberystwyth/Rhydlydan 33kV group under Option 1


16

Table 5-6: Option 1 costs and volumes


(£m) RIIO-ED2

Contribution(£m) 33kV UG Cable (Non-Pressurised) 12.15 2.948 2.948 33kV CB (Gas Insulated Busbars)(ID) (GM) 18 3.067 3.067

33kV Switch (GM) 1 0.047 0.047 Pilot Wire Underground 12 1.329 1.329 4x1.25MVAr MSC at Harlech 1 0.300 0.300 2x1.25MVAr MSC at Harlech 1 0.200 0.200 Civil Works at 33 kV & 66 kV Substations 0.670 0.670 Wayleaves/Easements/Land Purchase 0.800 0.800 Other Costs (Identify Below) 0.700 0.700

Total Costs 10.062 10.062 Power Quality assessment studies - £50k Environmental considerations and Design & Engineering Studies – £300k Associated protection, control or SCADA equipment -£250k River Crossing -£100k

5.4 Option 2 - ±10MVAr STATCOM at Aberdyfi and 5MVAr MSC at Harlech The Option 2 involves installing a ±10MVAr STATCOM at Aberdyfi and 5MVAr reactive compensation via installation of MSC at Harlech primary substation. The total cost of the scheme is £4.750m, including the flexible services procured for managing the network risks during scheme delivery. Table 5.7. Option 2 summary

Category Scheme Name Scheme Summary RIIO-ED2

Contribution (£m)


(£m)

Innovation Aberdyfi-Harlech 33kV Reinforcement



• Procure flexible services during delivery.

£4.750 -

Considering the above it is proposed to start the reinforcement works in 2023/24 and the capacity release of 15MVA will be claimed in 2026/27 at the end of the project. The costs of works under the Option 2 is shown in Table 5-8. Table 5-8: Option 2 solution costs


(£m) RIIO-ED2

Contribution(£m)

6.6/11kV CB (GM) Primary 1 0.028 0.028 33kV UG Cable (Non-Pressurised) 0.15 0.036 0.036

33kV CB (Gas Insulated Busbars)(ID) (GM) 5 0.852 0.852 33kV Transformer (GM) 1 0.314 0.314


2x2.5MVAr MSC at Harlech 1 0.250 0.250 Flexibility services - 0.138 0.138

Civil Works at 33 kV & 66 kV Substations 0.381 0.381 Wayleaves/Easements/Land Purchase 0.075 0.075

Other Costs (Identify Below) 0.167 0.167 Total Costs 4.750 4.750




17

5.5 Option 3- New 132kV 60MVA grid infeed at Aberdyfi The Option 3 involves installing a 60MVA grid infeed at Aberdyfi. The works include a new 132kV cable circuit from Rhydlydan to Aberdyfi ca. 25km long, and a new 60MVA grid transformer at Aberdyfi. The option also required additional 33kV switchgear to accommodate the grid transformer at Aberdyfi. The total cost of the scheme is £35.426m. The new grid infeed at Aberdyfi will increase the security of supply in the 33kV group as importantly

provided voltage support at Aberdyfi as well as the substations on the 33kV circuits emanating from

Aberdyfi. Table 5-9 and Table 5-10 provides the scheme summary and cost & volume breakdown

correspondingly. Figure 5.4 show the works included under the Option 3.

Table 5-9: Option 3 summary



Contribution (£m)


(£m)



1. New 25kms 132kV circuit between Rhydlydan – Machynlleth.

2. Extension of Machynlleth 33kV substation and installation of new 60MVA 132/33kV transformer at Machynlleth.

35.426 -

Aberdyfi

R

Aberystwyth Grid

R

R

R

Machynlleth

R

R

R

North Road

A

A

Llanilar

Fferm Wynt

Llangwyryfon

A

A

A

Rhydlydan Grid

Rheidol

Power

Station

A

Harlech

11kV7.5MVA

Dyffryn

Ardudwy

To

Maentwrog

Grid

303

220320 120

403

RHOS

ABERYSTWYTH

LLANARTH

110

T1103

CC3

NN136

NN138

NN242

NN335

NN334

NN243

103

Be/We

CC277A

CC277

CC91

CC90

CC4

NN344

213

T2

CC1

LAMPETER

110

T1

RHYDLYDAN

T1

113 CEFN CROES WIND FARM

T1113110MF1 MF121103105

Gn/Yw

Bk/We/Yw

NN137

Bk/Vt

Oe/We/Oe

~

60MW

132/33kV

60MVA Tx

132kV 400Sqmm

XLPE AL – 22kms

Figure 5.4: Works in Aberystwyth/Rhydlydan 33kV group under Option 3

Table 5-10: Option 3 costs and volumes


(£m) RIIO-ED2

Contribution(£m)

33kV CB (Gas Insulated Busbars)(ID) (GM) 7 1.193 1.193 33kV Switch (GM) 7 0.331 0.331

Batteries at 33kV Substations 1 0.009 0.009 132kV UG Cable (Non-Pressurised) 25 27.724 27.724

132kV Transformer 1 1.214 1.214 Batteries at 132kV Substations 1 0.008 0.008

Pilot Wire Underground 25 2.769 2.769 Civil Works at 33 kV & 66 kV Substations 0.365 0.365

Civil Works at 132 kV Substations 0.963 0.963 Wayleaves/Easements/Land Purchase 0.600 0.600

Other Costs (Identify Below) 0.250 0.250 Total Costs 35.426 35.426

Environmental considerations and Design & Engineering Studies – £50k Associated protection, control, or SCADA equipment -£200k


18

5.6 Options Cost Summary Table Summary of the costs for each of the evaluated options is presented in Table 5-11. Table 5-11: Costs summary for considered options

Options Considered Solution Costs(£m)

Baseline – 33kV circuit between Aberystwyth to Aberdyfi 9.083

Option 1- 33kV circuit between Bow Street to Aberdyfi 10.062

Option 2 - Innovation – STATCOM and MSC £4.750

Option 3 - New grid infeed at Aberdyfi 35.426

6 Deliverability & Risk 6.1 Preferred Options & Output Summary The adopted option is Option 2, to install a ±10MVAr STATCOM at Aberdyfi and 5MVAr MSC at Harlech to mitigate the voltage (steady state & step) issues in the group. It is also proposed to use flexibility services to minimize the network risk and support during the project delivery. The adopted solution is enduring, provides an additional uplift of 15MVA to the group and meet the demand growth in the group beyond RIIO-ED3.

6.2 Cost Benefit Analysis

A cost-benefit analysis was carried out to compare the NPV of the five options discussed in the previous sections. Considering the lowest forecast capital expenditure, the proposed option has the lowest total NPV and represents the lowest-cost option when losses and other operational costs are included in the analysis. Based on the outcome of the CBA, the proposed option is to install ±10MVAr STATCOM at Aberdyfi with 5MVAr MSC at Harlech along with operational risk management via flexibility services during project delivery is selected. The summary of the cost benefit analysis is presented in Table 6-1. The detailed costing of each of the options is provide in the cost benefit analysis document, “ED2-LRE-SPM-004-CV1-CBA – Aberdyfi-Harlech 33kV Reinforcement”. Table 6-1: Summary of Cost Benefit Analysis

Options considered Decision Comment

NPVs based on payback periods from 2023/24 (£m)

10 years

20 years

30 years

45 years

Baseline - New Circuit between Bow Street to Aberdyfi and MSC at Harlech

Rejected Discounted based high reinforcement cost.

£0.00 £0.00 £0.00 £0.00

Option1 -New Circuit between Bow Street to Aberdyfi and MSC at Tywyn and Harlech


-£0.55 -£0.75 -£0.87 -£0.96

Option2 -STATCOM at Aberdyfi and MSC at Harlech

Adopted This approach enables maximum benefit and value for customers money.

£2.89 £3.73 £4.23 £4.60

Option3 -New 132/33kV substation at Aberdyfi


-£14.32 -£19.47 -£22.52 -£24.85

6.3 Cost & Volumes Profile Table 6 2 shows the breakdown of expenditure for the proposed scheme (in 2020/21 prices) and the cost incidence (in 2020/21 prices) over the RIIO-ED2 period is shown in Table 6 3. The total cost of the proposed scheme is £4.750m.


19

Table 6-2: Summary of reinforcement Costs and Volumes, £m (2020/21 Prices)

Asset Description Volumes Prime Costs (£m) RIIO-ED2

Contribution(£m) 6.6/11kV CB (GM) Primary 1 0.028 0.028 33kV UG Cable (Non-Pressurised) 0.15 0.036 0.036

33kV CB (Gas Insulated Busbars)(ID) (GM) 5 0.852 0.852 33kV Transformer (GM) 1 0.314 0.314


2x2.5MVAr MSC at Harlech 1 0.250 0.250 Civil Works at 33 kV & 66 kV Substations 0.381 0.381

Wayleaves/Easements/Land Purchase 0.075 0.075 Other Costs (Identify Below) 0.167 0.167

Cost of flexibility services 0.138 0.138 Total Costs 4.750 4.750



Table 6-3: Summary of Allowed Expenditure under RIIO-ED2 (2020/21 Prices)

Investment category Total Incidence (£m)

(£m) 2023/24 2024/25 2025/26 2026/27 2027/28

CV1 (Primary reinforcement) 4.613 0.231 0.461 1.153 1.384 1.384

CV1(Flexible Services) 0.138 0.002 0.025 0.013 0.098 -

Total Cost 4.613 0.231 0.461 1.153 1.384 1.384

Derivation of costs for these options are based on the SPEN RIIO-ED2 Unit Cost Manual for intervention and cost estimates received from suppliers for STATCOM/MSC. This is based on bottom up cost assessment of the components of activity detailed within the RIGs Annex A for the above activities, SPEN’s contractual rates for delivery, market available rates and historic spend levels.

6.4 Risks The Aberystwyth and Rhydlydan 33kV network group is a sizeable both in terms of geographic expanse. As the group is forecast to experience both steady state and voltage step issues, the adopted option is a reactive compensation scheme through STATCOM and MSC installations to mitigate the issue. The network risk during project delivery will be operationally managed with support from flexibility services. STATCOM technology is well developed, has a technology readiness level of 9 (TRL9), however it is not a BaU solution in SPEN networks. MSC’s are also very well-established technologies and there are few MSC installations in the SPM network. The business will actively engage with the OEM suppliers and train relevant personnel for operational and maintenance. The operational expenditure for the STATCOM & MSC technologies is negligible as these have a very high reliability and availability with a very low replacement time of a failed module being <2Hrs. Both Aberdyfi and Harlech primary substations has 33kV AIS switchgear and there is ample space within the substations, so the installation does not require additional civil costs (e.g. building extensions etc).

6.5 Outputs Included in RIIO-ED1 Plans There are no outputs expected to be delivered in RIIO-ED1 that are funded within this proposal.


20

6.6 Future Pathways – Net Zero 6.6.1 Primary Economic Driver The primary driver for this investment is steady state and voltage step issues on the network around Aberystwyth, Aberdyfi, Tywyn, Machnylleth, Fairbourne, Harlech and Barmouth which will be beyond operational management due to the additional demand growth and LCT uptake. The investment does not have a strong reliance on environmental benefits. 6.6.2 Payback Periods The CBA indicates that a positive NPV result in all assessment periods (10, 20, 30 & 45 years) which are consistent with the lifetime of the intervention. As the intervention is forecast to carry at least a 45-year asset life expectancy, the positive CBA at this time justifies the intervention. Consumers benefit from reduced network risk immediately on completion of the project. 6.6.3 Sensitivity to Future Pathways The network capacity and capability that result from the proposed option has been tested against and has been found to be consistent with the network requirements determined in line with the section 9 of the Electricity Act and License Condition 21. Additionally, the proposed option is consistent with the SPENs DSO vision and future network strategy.

For the Aberystwyth / Rhydlydan 33kV group, Table 6.4 shows the electric vehicle and heat pump uptakes across a range of future pathways and Table 6.5 shows the sensitivity of the proposed solution and Table 6.6 shows the sensitivity of the proposed RIIO-ED2 expenditure against the full ranges of Net Zero complaint future pathways scenarios. Table 6.4: Electric Vehicle and Heat Pump uptakes across a range of future pathways

End of

RIIO-ED2

SPEN DFES CCC

Baseline System

Transformation* Consumer

Transformation

Leading the

Way

Balanced Net Zero

Headwinds Widespread Engagement

Widespread Innovation

Tailwinds

EVs 4,782 3,858 6,973 8,116 6,914 4,782 7,517 6,855 6,855

HPs 4,249 4,277 6,070 8,744 4,821 4,174 5,149 4,692 4,591 * Note: We have excluded System Transformation from our future pathways assessment as it does not meet interim greenhouse gas emission reduction targets.

Table 6.5: Sensitivity of the proposed solution against future pathways

Solution Requirements

RIIO-ED1 RIIO-ED2 RIIO-ED3

202

0

202

1

202

2

202

3

202

4

202

5

202

6

202

7

202

8

202

9

203

0

203

1

203

2

203

3

Baseline R1 Consumer Transformation R1 R2 Leading the Way R1 Balanced Net Zero R1 R2 Headwinds R1

Widespread Engagement R1 R3 Widespread Innovation R1 R2 Tailwinds R1 R2

R1 – Proposed solution - Reactive Compensation (±10MVAr STATCOM & 5 MVAr MSC) R2– Additional 33kV circuit between Aberystwyth and Aberdyfi

R3– Additional 132/33kV grid infeed The proposed ‘smart’ solution is expected to provide sufficient capacity to cater for network requirements beyond RIIO-ED2 and well into ED3 across all scenarios. The timing of the RIIO-ED2 requirement is sensitive to the volume of LCT uptakes but is required by the end of RIIO-ED2 in all scenarios. A collaborative Whole Systems planning approach is required to identify the optimal long-


21

term Distribution/Transmission solutions to upgrade the mid-Wales networks to meet long term demand and generation requirements and be Net Zero ready. Table 6.6: Sensitivity of the proposed RIIO-ED2 expenditure

Baseline Uncertain

RIIO-ED2 Expenditure (£m) 4.750 0 Comment Proposed option. N/A

6.6.4 Asset Stranding Risks & Future Asset Utilisation Electricity demand and LCT uptake are forecast to increase under all scenarios. As the proposed solution comprises of packaged reactive support device which provides flexibility and can be relocated and reused elsewhere in the network, hence asset stranding risk is low. 6.6.5 Losses / Sensitivity to Carbon Prices Losses have been considered in accordance with License Condition SLC49 and the SP Energy Networks Losses Strategy and Vision to “consider all reasonable measures which can be applied to reduce losses and adopt those measures which provide benefit for customers”. Reasonable design efforts have been taken to minimise system losses without detriment to system security, performance, flexibility or economic viability of the scheme. Losses have not been evaluated as part of optioneering the optimum solution for the scheme. As the proposed scheme involves reactive compensation equipment which is primarily to support the voltage issues in the grid group, the impact of the voltage support on the network losses involves a complex network analysis. As such. the detailed losses assessment will be carried out during the design stage of the proposed scheme.

6.7 Environmental Considerations It has been assessed that the preferred option is consistent with the future generation and demand scenarios and that the risk of stranding is very low.


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7 Conclusion The Aberdyfi and Harlech areas of the SP Manweb network lie within the Aberystwyth / Rhydlydan 33kV group which supplies over 22,600 customers predominantly fed from long overhead line circuits. The group is presently at voltage limits and at risk of marginal voltage excursions outside of statutory limits, it is presently being operationally managed. The adopted option is a strategic and innovative solution, proposed to install reactive power compensation devices at Aberdyfi and Harlech primary substations in the RIIO-ED2 period in order to mitigate the voltage violations and maintain the steady state voltage of the 33kV network to within ±6% of the declared voltage under the ESQCR 2002 and maintain voltage step within ±10%. The proposed solution represents the lowest cost and most efficient engineering solution to meet the forecast demand growth when compared with the alternative schemes identified. In order to accommodate additional demand from LCT uptake and mitigate the steady state and voltage step risk a strategic reinforcement scheme with innovative solution is proposed. The recommended solution comprises:



• Procure flexible services to manage the network risk during the scheme delivery.

The voltage constraints in this group are both steady state and voltage step. These voltage step issues cannot be mitigated through flexibility as the mitigation needs to be fast acting in real-time. Thus, it is proposed to use flexibility services to minimize the steady-state network risk and support during the project delivery. We will continue to tender for flexibility services in this area to test the market for technically compliant flexibility solutions to resolve this complex voltage constraint.

It is proposed to start the works in 2023/24 and the capacity release of 15MVA between the two 33kV groups will be claimed in 2027/28 at the end of the project. The timing of the project is based on delivering the highest NPV, while managing the network risk via operational management through flexibility services during project delivery.

Total scheme cost – £4.750m (2020/21 prices) with 100% contribution to be included in the RIIO-ED2 load related expenditure.


23

8 Appendices 8.1 Profile based study results The post operational management voltages calculated based on half hourly profile-based simulations using historical SCADA data are shown below:

2023/24 MarApr May Jun Jul Aug Sep Oct Nov Dec Jan Feb

0.00 2.02.00 0.0 5.0

00:00 - 02:30

03:00 - 05:30

06:00 - 08:30

09:00 - 11:30

12:00 - 14:30

15:00 - 17:30

18:00 - 20:30

21:00 - 23:30

11.00 7.000.00 0.00 0.00 0.00 0.00

Ris

k D

ura

tio

n =

27 H

rs


0.00 8.02.50 4.0 12.0

00:00 - 02:30

03:00 - 05:30

06:00 - 08:30

09:00 - 11:30

12:00 - 14:30

15:00 - 17:30

18:00 - 20:30

21:00 - 23:30

12.50 4.500.00 0.00 0.00 0.00 0.00

Ris

k D

ura

tio

n =

43.5

Hrs


0.00 20.511.00 7.5 30.0

00:00 - 02:30

03:00 - 05:30

06:00 - 08:30

09:00 - 11:30

12:00 - 14:30

15:00 - 17:30

18:00 - 20:30

21:00 - 23:30

17.50 18.000.00 0.00 0.00 0.00 0.00R

isk D

ura

tio

n =

104.5

Hrs


0.00 52.5112.00 69.0 123.5

00:00 - 02:30

03:00 - 05:30

06:00 - 08:30

09:00 - 11:30

12:00 - 14:30

15:00 - 17:30

18:00 - 20:30

21:00 - 23:30

42.50 109.500.00 0.00 0.00 0.00 0.00

Ris

k D

ura

tio

n =

509 H

rs


0.00 201.0235.50 250.5 271.5

00:00 - 02:30

03:00 - 05:30

06:00 - 08:30

09:00 - 11:30

12:00 - 14:30

15:00 - 17:30

18:00 - 20:30

21:00 - 23:30

56.00 178.500.50 0.00 0.50 0.00 0.00

Ris

k D

ura

tio

n =

1194 H

rs

Voltage (p.u)

1.00########## 0.9### 0.9####### 0.80

0.94


24

8.2 Aberdyfi and Harlech – Sites and proposed equipment 8.2.1 Aberdyfi primary substation

Figure 8.1: Aerial view of Aberdyfi 33kV substation

Figure 8.2: STATCOM single line diagram and layout


25

8.2.2 Harlech primary substation

Figure 8.3: Aerial view of Harlech 33kV substation

Figure 8.4: Typical arrangement of Enclosed Capacitor Bank


26

8.3 STATCOM Datasheet STATCOM Datasheet

Rated capacity 10Mvar

Nominal voltage level 11kV

Ambient temperature -20~+50°C

Relative humidity 100%

Cooling Water cooled

Maximum continuous operating capacity 11Mvar

Temporary overload capacity (10s) 12Mvar

Minimum operating voltage capability 0.2 pu. / 10s

Step-change response <100ms

Maximum overshoot <10%

Continuous Operating frequency range 47~53Hz

Installation Type Container（Valve & control container）

Valve container size：13500*3100*3000mm (LWH)

Valve container weight：22t

STATCOM Controller

Controller Digital programmable controller using Control System

Control Modes Slope based voltage controller, Constant Reactive Power, LVRT, HVRT

Reference voltage 0.9pu – 1.1pu

Slope 1.0%-5.0% (0.1% steps)

STATCOM Valve

No. of Phase Branches per Valve 3

Rated STATCOM reactive power ±10 MVAr

Nominal frequency 50 Hz

Nominal voltage level 11kV

Three phase converter type Y (Star)

Rated Current (phase) 0.525kA

Series Number of Power Module per phase 5

Redundancy of Power Module per phase 1

TOTAL number of Power Modules per phase 6

The frequency of PWM switching of PP-IGBT 350Hz

Short-term overload [1.2x 10s] depending on overload selection

Insulation to Earth 17.5kV

STATCOM Power Module

Power Module nominal DC voltage 2200-2650 V

Power Module nominal AC output voltage (RMS) 1540-1874V

PM maximum DC voltage 3000 V

No of IGBT per PM 4

No of DC capacitor per PM 1

PM total weight 230kg

PM power block weight 100kg

PM DC capacitor weight 90kg

IGBT Ratings

VCE 4500 V

ICP 3000 A

DC Capacitor

Rated Capacitance 4000 μF

Rated Voltage 2800 V

Maximum rms current 750 A

1.15pu Overvoltage 30 minutes

1.3pu Overvoltage 1 minute

STATCOM Cooling

Type of cooling Closed loop deionised water with forced air external heat exchanger. No make-up needed for normal cooling operation. Integrated deionisation loop.

Material 304 and 316L

Pumps Main and standby centrifugal main pump

Heat exchangers 1 heat exchangers each with 3 fans.

STATCOM Protection

Main Protection (RXHK HUIC Controller) Over-current, Differential current, Controller fault, Communication Fault, Loss of synchronization fault, emergency stop, bypass fault, HV switch abnormal operation fault, overvoltage, undervoltage. Breaker failure

Backup Protection (by others) Feeder over-current, earth-fault, breaker failure.

STATCOM Auxiliary Supplies Required

LVAC (single or dual) 3-phase, 50Hz, 415V,

LVDC (dual supplies) 110VDC,

Capacity Required LVAC 30kVA LVDC 10A

STATCOM SCADA Interface

Local HMI Included as panel mounted IPC with screen and keyboard

Remote SCADA TCP/IP via Fibre IEC104/IEC61850/DNP3/Modbus

STATCOM Maintenance

Routine Service Annual

Time to replace failed module 2hrs

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